As is conventionally known, a stern drive (also referred to as an inboard engine—outboard drive) includes an engine provided inboard, and a drive unit provided outboard that transmits power from the engine to a propeller. Further, a cooling system for such a stern drive is also conventionally known. Such a cooling system cools the drive unit by spraying water onto a housing of the drive unit. The water is taken from ambient water of the drive unit, and the water is discharged using water pressure generated by the propulsive speed due to the so-called ram effect.
For example, U.S. Pat. No. 6,808,432, which was issued to Richard A. Davis et al. on Oct. 26, 2004, teaches providing a cover to a housing of a drive unit, and using a cooling unit that discharges water through an outlet on the top of the housing where a gear that generates heat is contained, using ram pressure. However, this cooling system has the following defect. A general housing contains oil to be used as a lubricating oil, or as a hydraulic fluid for operating the hydraulic clutch when a hydraulic clutch is provided. The oil level is enough to soak the gear in the housing, and the space between the oil level and the internal top of the housing has low heat conductivity. In other words, this space serves as a heat insulator. Therefore, the cooling system disclosed in U.S. Pat. No. 6,808,432 does not ensure desirable cooling efficiency.
U.S. Pat. No. 5,871,380, which was issued to Dean Claussen on Feb. 16, 1999, teaches an intercooler for a stern drive using a water jacket, which is provided on the back of the housing, where a gear that generates heat is provided.
However, in this invention, water accumulates in the water jacket, increasing the water pressure inside the water jacket. This inhibits the ram effect. This invention also, therefore, does not ensure desirable cooling efficiency.